An ejector or venturi may be used as a vacuum source in dual path purging systems in an engine for fuel vapor recovery. For example, an inlet of an ejector may be coupled to an engine intake upstream of a compressor via a hose or duct and an outlet of the ejector may be coupled to an intake of the engine downstream of the compressor via a hose or other conduit. Motive fluid through the ejector provides a vacuum at an ejector suction inlet which may be coupled to a fuel vapor canister to assist in purging the fuel vapor canister during boosted operation.
If the ejector develops a leak, or if any of the hoses coupling the ejector to the compressor inlet or outlet becomes disconnected or degraded, exhaust hydrocarbons may escape to the atmosphere, rendering the vehicle emissions non-compliant. To address this issue, the integrity of the purge ejector is intermittently diagnosed. One example approach for diagnosing the ejector is shown by Plymale et al. in US 2014/0251284. Therein, leaks due to stresses to the ejector and/or degradation in ejector system components, such as hoses or ducting, are diagnosed upstream of an inlet to the ejector based on insufficient boost pressure and/or insufficient ejector vacuum generation. To reduce leaks due to hose disconnection downstream of the ejector outlet (that is, between the ejector and the air induction system (AIS)), a shut-off valve is directly mounted (e.g., via spin welding) to the AIS and coupled to the ejector outlet.
However the inventors herein have identified potential issues with such approaches. As one example, in spite of the direct mounting, the ejector may still break at the AIS or assembly plant. Alternatively, a service technician may remove it during servicing and forget to reinstall it. In any of these situations, hydrocarbons may be released into the atmosphere, undetected, during boosted purge by the ejector of Playmale. Further, if the ejector fails, in addition to the ejector, the entire AIS will need to be replaced since the ejector is directly mounted on the AIS. As such, this may add to warranty costs. The inventors have also recognized that only the upstream portion of the boosted purge line is diagnosed, and that the downstream portion of the boosted purge line remains undiagnosed. In other words, the above-discussed approach may not be able to detect a fault if the line between the ejector and the compressor inlet is disconnected or leaking.
To address at least some of the above issues, a method for diagnosing a purge ejector is provided. The method includes, indicating disconnection of an ejector coupled in a boosted purge path between a fuel vapor canister and a compressor inlet based on exhaust air-fuel ratio during boosted purge relative to exhaust air-fuel ratio during vacuum purge of the canister. In this way, a purge ejector may be diagnosed without relying on additional sensors or hardware.
As an example, in response to purging conditions being met, such as upon confirming that a fuel system fuel vapor canister is sufficiently loaded with hydrocarbons (e.g., after a refueling event), the canister may be purged under engine vacuum. A controller may monitor for a rich exhaust air-fuel ratio response at an exhaust gas sensor (e.g., a UEGO sensor) during the purge with natural aspiration. Purge is then suspended and the canister load is updated. Next, during boosted engine operation, the canister is purged under boost. If the exhaust gas sensor continues to show a rich exhaust air-fuel ratio response (that is, richer than stoichiometry) during the boosted purge, it may be determined that the ejector is not degraded. However, if the exhaust gas sensor does not show a rich response during the boosted purge (e.g., the exhaust air-fuel ratio is stoichiometric or leaner than stoichiometry), it may be determined that the ejector is degraded and that hydrocarbons are not entering the intake manifold. For example, it may be determined that the ejector is broken, clogged, or disconnected.
The technical effect of comparing an exhaust gas sensor response during vacuum purge of a purge ejector to the exhaust gas sensor response during boosted purge of the purge ejector is that it may be confirmed that the ejector is still mounted to the intake manifold housing at the compressor inlet and that hydrocarbons are not escaping to the atmosphere. In particular, a purge ejector coupled (e.g., directly mounted) in a boosted purge line may be diagnosed at the downstream location (proximate to the compressor inlet) based on changes in an exhaust air-fuel ratio incurred during purge through each path of a dual path purge system without requiring additional sensors, ducting, or other hardware. By improving purge system diagnostics at both the upstream and downstream end of the ejector, a boosted purge path may be accurately diagnosed, and exhaust emissions compliance of a boosted engine can be improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.